[PATCH] models: Add State.slug field

[Stephen Finucane]

On Sun, 2019-12-08 at 16:00 +0000, Stephen Finucane wrote:
> This reduces a lot of the tech debt we had built up around this. This
> field is populated from a slugified representation of State.name and has
> a uniqueness constraint. As a result, we also need to a uniqueness
> constraint to the State.name field. This shouldn't be an issue and
> probably should have been used from day one.
> 
> Note that there is no REST API impact for this since we've been using
> state slugs all along.
> 
> Signed-off-by: Stephen Finucane <stephen at that.guru>

Applied.